updated readme with android external storage permission

README.md

 |`reminder`| ✔️ | ❌ |
 |`notification`| ✔️ | ❌ |
 |`backgroundRefresh`| ✔️ | ❌ |
+|`storage`| ❌️ | ✔ |
 
 ###Methods
 | Method Name | Arguments | Notes
 `camera` -> `android.permission.CAMERA`  
 `microphone` -> `android.permission.RECORD_AUDIO`  
 `photo` -> `android.permission.READ_EXTERNAL_STORAGE`  
+`storage` -> `android.permission.READ_EXTERNAL_STORAGE`  
 `contacts` -> `android.permission.READ_CONTACTS`  
 `event` -> `android.permission.READ_CALENDAR`